Modal Comparison of Stock and Performance Brake Rotors

Abstract

Although generally similar in appearance, automobile brake rotors vary widely in terms of cost, material, and quality. Modal analysis was conducted on a variety of stock and performance used and new brake rotors to determine whether vibration analysis could be an effective method for evaluating quality, performance, and/or remaining life of a given brake rotor. Regular and slotted performance brake rotors were tested using an impact hammer and tri-axial accelerometer, and natural frequencies were evaluated up to 12,000 Hz. Testing methodology was varied to determine what parameters were most effective to highlight differences between rotors. The overall finding was that the most significant difference between rotors was due to the reduced mass of a used rotor; i.e., different types of rotors for the same vehicle showed greater similarity in dynamic response than a new rotor and a used rotor of the same type. Additionally, comparison of new and used rotors can show a correlation between remaining rotor life and dynamic response. While simple mass measurement of the rotor could provide similar information, vibration data can be taken with the brake rotor in place on the vehicle, and could provide information about the amount of brake rotor used in high performance driving events during the event, as well as the condition of the rotor. Testing is ongoing, and may also include identification of dynamic response for cracked rotors. Further testing is required to verify the differences in rotor wear for rotors installed on the vehicle.